Mitochondrial DNA analysis of the bark beetle predator Thanasimus dubius F. (Coleoptera: Cleridae) reveals regional genetic differentiation

The checkered beetle, Thanasimus dubius F., is an important predator of scolytid bark beetles that attack conifers. Relatively few studies exist that have addressed the population genetics of predatory beetles, especially those with potential as biological control agents. This study was conducted to investigate the population genetics of T. dubius across a large part of its range in the eastern United States. A 464-base pair portion of the mitochondrial cytochrome c oxidase subunit I was sequenced for 85 individuals resulting in 60 haplotypes. Analysis of molecular variance was conducted on the resulting haplotypes for all populations and as a hierarchical analysis between populations defined as broad-scale northern and southern groups. Results indicate a significant overall Phi ST = 0.220 (P < 0.001) for all populations with the hierarchical analysis revealing that this significant Phi ST is due to structuring of the populations between northern and southern regions (Phi CT = 0.388, P < 0.009). The observed genetic structure is possibly due to the discontinuous distribution of pine trees, which act as hosts for the prey of T. dubius, which has occurred historically in the central region of the United States that has been covered by prairie.     

Complex emergence patterns in a bark beetle predator

1 The emergence pattern of Thanasimus dubius (F.) (Coleoptera: Cleridae), a common predator of the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), was studied under field conditions across different seasons. A simple statistical model was then developed to characterize the emergence data, using the truncated geometric distribution. Data are also presented on the mortality of T. dubius eggs at various temperatures and humidities in an effort to explain certain aspects of emergence behaviour. 2 Emergence of T. dubius from a given tree usually occurred in several discrete episodes across a two‐year period, with most individuals emerging in spring or autumn. Almost no emergence occurred in July and August, which may be an adaptation to avoid high temperature mortality. Emergence patterns appeared similar across seasons, with the time of year serving mainly to shift the pattern through time. 3 Cycles in D. frontalis abundance may be the result of delayed density dependence generated by its natural enemy complex. The predator T. dubius is likely to be an important component of this delayed density dependence, because of its lengthy development time and apparent impact on D. frontalis.     

Differences in photoperiod‐induced diapause plasticity among different populations of the bark beetle Ips typographus and its predator Thanasimus formicarius

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Integration of visual and olfactory cues of hosts and non-hosts by three bark beetles (Coleoptera: Scolytidae)

Abstract.  1. There has been a long-standing pre-occupation with how phytophagous insects use olfactory cues to discriminate hosts from non-hosts. Foragers, however, should use whatever cues are accurate and easily assessed, including visual cues.
2. It was hypothesised that three bark beetles, the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, the Douglas-fir beetle (DFB), D. pseudotsugae Hopkins, and the western balsam bark beetle (WBBB), Dryocoetes confusus Swaine, integrate visual and olfactory information to avoid non-host angiosperms (e.g. paper birch, trembling aspen), that differ in visual and semiochemical profile from their respective host conifers (lodgepole pine, Douglas-fir, interior fir), and tested this hypothesis in a series of field trapping experiments.
3. All three species avoided attractant-baited, white (non-host simulating) multiple-funnel traps, and preferred attractant-baited black (host-simulating) traps. In experiments combining white, non-host traps with non-host angiosperm volatiles, bark beetles were repelled by these stimuli in an additive or redundant manner, confirming that these species could integrate visual and olfactory information to avoid non-host angiosperms while flying.
4. When antiaggregation pheromones were released from white traps, the DFB and MPB were repelled in an additive-redundant manner, suggesting that beetles can integrate diverse and potentially anomalous stimuli.
5. The MPB demonstrated the most consistent visual preferences, suggesting that it may be more of a 'visual specialist' than the DFB or WBBB, for which visual responses may be more contingent on olfactory inputs.     

Close-range, in-flight integration of olfactory and visual information by a host-seeking bark beetle

A long‐standing controversy questions whether foraging bark beetles assess the suitability of individual host trees using cues at close range while flying or engage in random landing followed by contact assessment. In most cases, visual discrimination mechanisms are ignored. We show that pheromone‐responding mountain pine beetles (MPB), Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae), can visually discriminate between ‘host’ (black) and ‘non‐host’ (white) traps arranged in small clusters, in the absence of additional host olfactory information, and that males (but not females) demonstrate a greater preference for combined host visual and olfactory cues. However, white, non‐host traps baited with a host volatile were as attractive as unbaited, black host traps. Our results support the hypotheses that when deciding to land, the MPBs integrate visual and olfactory information and can process cues in both sensory modes at relatively close range (≤2 m). Thus, host selection mechanisms in this species are unlikely to be random with respect to either sensory mode.     

Escape trajectories of the rockpool prawn (Palaemon elegans) in response to visual and mechanosensory stimuli

Small crustaceans, such as the rockpool prawn Palaemon elegans Rathke, respond to the approach of predators by executing a version of the crustacean tail-flip response, known as the ‘jack-knife’. We used two types of stimulus to investigate the escape behaviour of P. elegans, specifically the escape trajectories taken by individual prawns. The first stimulus consisted of mechanosensory cues, while the second stimulus included visual and mechanosensory cues. Responses to the two stimulus types differed, with the combined cues from the second stimulus type resulting in escapes over longer distances, and with greater directionality, compared to those following purely mechanosensory stimulation. Altering the direction of approach of the ‘predator’ affected the proportion of escapes that were to the side opposite from the eliciting stimulus and strongly influenced escape trajectories. Such unpredictability in the escape direction of P. elegans may be an example of so-called ‘Protean’ behaviour.     

Responses to olfactory and visual cues by over-wintered and summer generations of the pollen beetle, Meligethes aeneus

Abstract.  Behavioural responses to odours of oilseed rape in bud and flower stage and to green and yellow colours are studied for the two main phenological stages of pollen beetles, Meligethes aeneus , a major pest of oilseed rape, Brassica napus . Over-wintered individuals oviposit in buds of oilseed rape. Adults of the new generation (i.e. the summer generation) feed on flowers of different plant species before over wintering. In olfactometer experiments, the over-wintered beetles display a higher preference for odour of oilseed rape at the bud stage compared with the summer generation, both with and without colour stimuli. Flower odours are preferred in combination with yellow colour. Colour stimuli presented alone do not affect the behaviour. The summer generation beetles respond to both bud and flower odour. Adding colour stimuli changes the summer generations preference towards yellow and flower odour.     

Effect of varying monoterpene concentrations on the response of Ips pini (Coleoptera: Scolytidae) to its aggregation pheromone: implications for pest management and ecology of bark beetles

Abstract 1 Host plant terpenes can influence attraction of conifer bark beetles to their aggregation pheromones: both synergistic and inhibitory compounds have been reported. However, we know little about how varying concentrations of individual monoterpenes affect responses. 2 We tested a gradient of ratios of α‐pinene, the predominant monoterpene in host pines in the Great Lakes region of North America, to Ips pini's pheromone, racemic ipsdienol plus lanierone. 3 Ips pini demonstrated a parabolic response, in which low concentrations of α‐pinene had no effect on attraction to its pheromone, intermediate concentrations were synergistic and high concentrations were inhibitory. These results suggest optimal release rates for population monitoring and suppression programmes. 4 Inhibition of bark beetle attraction to pheromones may be an important component of conifer defences. At terpene to pheromone ratios emulating emissions from trees actively responding to a first attack, arrival of flying beetles was low. This may constitute an additional defensive role of terpenes, which are also toxic to bark beetles at high concentrations. 5 Reduced attraction to a low ratio of α‐pinene to pheromone, as occurs when colonization densities become high and the tree's resin is largely depleted, might reflect a mechanism for preventing excessive crowding. 6 Thanasimus dubius, the predominant predator of I. pini, was also attracted to ipsdienol plus lanierone, but its response differed from that of its prey. Attraction increased across all concentrations of α‐pinene. This indicates that separate lures are needed to sample both predators and bark beetles effectively. It also provides an opportunity for maximizing pest removal while reducing adverse effects on beneficial species. This disparity further illustrates the complexity confronting natural enemies that track chemical signals to locate herbivores.     

The role of beetle and host volatiles in host colonization in the European oak bark beetle, Scolytus intricatus (Ratzeburg) (Col., Scolytidae)

Abstract:  To understand the role of chemical signals involved in Scolytus intricatus (Ratzeburg) (Col., Scolytidae) host colonization, the attractiveness of intact and beetle colonized host material was investigated in the field and in the laboratory. In the field, chemical signals operating at long range were investigated by means of sticky traps. In the laboratory, close-range chemical interactions were investigated with an arena olfactometer. Field experiments showed no differences in the attractiveness between infested and non-infested host material. On the contrary, laboratory experiments revealed higher attractiveness of infested host and beetle-produced frass in comparison with intact host and mechanically produced sawdust respectively. Laboratory data also disclosed the attractiveness of beetle extracts of both sexes. Our data show that: (1) host kairomones play an important role during host colonization, and that (2) S. intricatus does not use a sex-specific secondary attractant system. Differences between results of field and laboratory trials are discussed.     

Effects of tree mortality caused by a bark beetle outbreak on the ant community in the San Bernardino National Forest

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Selective manipulation of predators using pheromones: responses to frontalin and ipsdienol pheromone components of bark beetles in the Great Lakes region

Abstract 1 One proposed approach to improving biological control of bark beetles (Coleoptera: Scolytidae; alt. Curculionidae: Scolytinae) is to manipulate predator movement using semiochemicals. However, selective manipulation is impeded by attraction of both predators and pests to bark beetle pheromones. 2 The primary bark beetle affecting pine plantations in Wisconsin, U.S.A., is the pine engraver, Ips pini (Say). Other herbivores include Ips grandicollis (Eichhoff) and Dryophthorus americanus Bedel (Curculionidae). The predominant predators are the beetles Thanasimus dubius (Cleridae) and Platysoma cylindrica (Histeridae). 3 We conducted field assays using two enantiomeric ratios of ipsdienol, and frontalin plus α‐pinene. Ipsdienol is the principal pheromone component of I. pini, and frontalin is produced by a number of Dendroctonus species. α‐Pinene is a host monoterpene commonly incorporated into commercial frontalin lures. 4 Thanasimus dubius was attracted to frontalin plus α‐pinene, and also to racemic ipsdienol. By contrast, I. pini was attracted to racemic ipsdienol, but showed no attraction to frontalin plus α‐pinene. Platysoma cylindrica was attracted to 97%‐(–)‐ipsdienol and, to a lesser extent, racemic ipsdienol, but not to frontalin plus α‐pinene. Ips grandicollis was attracted to frontalin plus α‐pinene but not to ipsdienol. Dryophthorus americanus was attracted to both ipsdienol and frontalin plus α‐pinene. 5 This ability to selectively attract the predator T. dubius without attracting the principal bark beetle in the system, I. pini, provides new opportunities for research into augmentative biological control and basic population dynamics. Moreover, the attraction of T. dubius, but not P. cylindrica, to frontalin plus α‐pinene creates opportunities for selective manipulation of just one predator. 6 Patterns of attraction by predators and bark beetles to these compounds appear to reflect various degrees of geographical and host tree overlap with several pheromone‐producing species.     

Prolonged development time of the bark beetle predator Thanasimus formicarius (Col.: Cleridae) in relation to its prey species Tomicus piniperda (L.) and Ips typographus (L.) (Col.: Scolytidae)

1 The generation time of the bark beetle predator Thanasimus formicarius (L.) (Col.: Cleridae) was found to be predominantly two years both in the field and in rearing experiments conducted with two of its main prey species, the pine shoot beetle Tomicus piniperda (L.) and the spruce bark beetle Ips typographus (L.) (Col.: Scolytidae). 2 Emergence of T. formicarius adults in the first summer was only observed in one of the two rearing experiments, and these individuals represented only 6% of that generation. 3 All individuals not emerging as adults in the first summer remained as larvae in their pupal chambers until the second summer. Pupae were found starting around mid-June, and adults (in pupal chambers) were found from late July through to the end of August. 4 Newly emerged adults had to feed in order to survive hibernation. 5 The existence of T. formicarius races, specialized on certain bark beetle species and with phenologies matching their hosts, could not be demonstrated. After hibernation there was no difference in feeding activity, timing of egg-laying or proportion of egg-laying females between the T. formicarius adults reared as larvae on T. piniperda (flight period in April) and those reared as larvae on I. typographus (main flight period generally starting in late May or early June) when exposed to a temperature and day-length typical of the early spring conditions prevailing during the flight period of T. piniperda. 6 T. formicarius was parasitized by Enclisis vindex (Tschek) (Hym.: Ichneumonidae) in the pupal chamber. 7 The importance of these findings for the population dynamics of bark beetles is discussed.     

Flight behaviour of Encarsia formosa in response to plant and host stimuli

The flight behaviour of Encarsia formosa Gahan (Hymenoptera: Aphelinidae), a parasitoid of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) has been studied in response to the following natural components: bean plant (Phaseolus vulgaris L.) infested with T. vaporariorum (PHC, plant host complex), host damaged bean plant from which whiteflies were removed (HDP, host damaged plant), T. vaporariorum third instar larvae (H, host), uninfested bean plant (P, plant) and T. vaporariorum empty pupal cases (EPC, empty pupal cases). A combination of chemical and visual stimuli is necessary in host location from a distance by E. formosa and seems to deeply affect the dispersal of this parasitoid. The presence of host (PHC, H) or of its parts (EPC) led to a substantial increase of oriented flights suggesting the occurrence of host derived chemicals. At a closer range, a combination of visual and chemical stimuli deriving from all the components of the plant host complex elicited the transition flying-landing and the following landing on the source.     

Flight propensity and diapause incidence in five populations of the bark beetle Ips typographus in Scandinavia

Emergence from brood logs, take-off activity and the duration of tethered flight was recorded in the first laboratory generation of the bark beetle Ips typographus L. (Coleoptera: Scolytidae) from five locations (ca 300 km apart) in Sweden and Denmark. Beetles of northerly origin emerged later from brood logs. This pattern was associated with an increasing proportion on non-fliers towards the north. After overwintering, both the rate of development of flight activity and the proportion of non-fliers were the same among populations. Flight duration of fliers was similar among populations and appeared unaffected by outbreak conditions.     

The effect of host odour on the landing responses of tsetse flies (Glossina morsitans morsitans) in a wind tunnel with and without visual targets

Abstract The effect of artificial host odour on the landing responses of males of Glossina m.morsitans West, and on their reaction to visual targets has been investigated in a wind tunnel. Landing was induced in flies that traversed steep odour gradients as they flew upwind and downwind across the edge of an odour plume, irrespective of whether visual targets were present or not; the landing response could be elicited over a wide range of odourconcentrations. When targets were present such odour gradients also tended to increase the proportion of landing flies which alighted on or near the targets; and the bigger the target, or the hungrier the flies, the greater was the propensity for target landing. In air which was more uniformly permeated with odour, the propensity to land on targets was increased only at high odour concentration.     

Influence of visual and olfactory cues on field trapping of the pollen beetle, Astylus atromaculatus (Col.: Melyridae)

Field trapping experiments investigated the response of the pollen beetle Astylus atromaculatus to visual and olfactory cues during a 3-year period, 1999–2001. The visual preference of the pollen beetle was determined using yellow, white, blue, green and red water traps. The yellow trap was most attractive, capturing 56% of the total beetles trapped, with 30% caught by the blue and white traps, while 14% was caught by the red and green traps. The response of the beetle to olfactory cues was then evaluated by using the yellow water trap with three antennally active components identified in the volatiles of sorghum panicles by coupled gas chromatography (GC)–electroantennographic detection and GC–mass spectrometry. These components were 2-phenylethanol, benzyl alcohol and linalool. There were no significant colour × chemical compound interactions and traps baited with 2-phenylethanol captured significantly more beetles than unbaited traps, irrespective of trap colour, demonstrating the effectiveness of olfactory cues in trapping the pollen beetle. Traps baited with 2-phenylethanol were more attractive than and caught more beetles than traps baited with linalool. 2-Phenylethanol had the greatest effect on the relatively unattractive blue trap, confirming the importance of olfactory cues mediating A. atromaculatus attraction .     

Orientation responses of the grasshopper, Melanoplus sanguinipes, to visual, olfactory and wind stimuli and their combinations

Prereproductive adults of the grasshopper, Melanoplus sanguinipes (F.) (Orthoptera, Acrididae), demonstrated orientation and movement towards both visual and olfactory stimulus sources in a still-air chamber. Visual stimuli (wheat and lima bean foliage, vertical black or yellow-green stripes, and a yellow-green broad leaf pattern) were approached more frequently than the control white background surface. Olfactory stimuli (chopped wheat foliage and a four-component, synthetic, grass odor blend of volatiles) elicited an even greater positive response than the visual stimuli. Changing the proportions of the four volatiles in the blend significantly reduced positive orientation responses to the stimulus source. Visual cues of wheat foliage and olfactory cues of either chopped wheat odor or the grass odor blend gave greater responses when combined than when presented separately.In flowing air or wind, nearly all insects demonstrated a rapid positive response to odors of chopped wheat and the grass odor blend, significantly greater than the response to the same stimuli in still air. However, positive responses to visual cues were not significantly greater in wind than in still air. When combined with the olfactory stimuli in flowing air, visual cues did not increase the incidence of response. Grasshoppers responding to grass odors in wind moved more rapidly and directly toward the source, and stopped less often and for shorter durations than insects responding to odor in still air or to visual cues.We conclude from these studies that M. sanguinipes adults show orientation behavior to both visual and olfactory stimuli from food plant sources, although leaf odors elicit a stronger positive response particularly when carried by wind.     

Effects of wind on movement of Diachasmimorpha longicaudata, a parasitoid of tephritid fruit flies, in a laboratory flight tunnel

Cohorts of mass-reared adult female Diachasmimorpha longicaudata (Ashmead), parasitoids of tephritid fruit fly larvae, were released in a laminar air flow wind tunnel to study the effects of air movement on flight and walking behaviors. Wind in the tunnel was cycled on and off at intervals to simulate gusty conditions observed in the field. Wind speed influenced parasitoid movement during both the wind-on periods and during the calm intervals between gusts. Wind speeds of 0.8 m per second suppressed flight and walking behaviors, while wind speeds of 0.4 m/s stimulated both flight and walking behaviors. There was an exponential increase in the ratio of activity in calm to activity in wind as wind speed increased.     

Relevance of visual and olfactory cues for host location in the mustard leaf beetle Phaedon cochleariae

The relevance of visual and olfactory cues for host‐plant location is investigated in males and females of the oligophagous mustard leaf beetle Phaedon cochleariae Fabricius (Coleoptera: Chrysomelidae). Different objects are offered in a walking arena and the behaviour of beetles is observed. Beetles orient toward vertically or horizontally striped black and white pattern independent of stripe orientation. The results suggest that contrast facilitates orientation in the field, whereas the pattern itself may be less important for host location in dense vegetation. The response to green and yellow objects is tested to investigate discrimination abilities between young (green) and mature (yellow) leaves. Beetles prefer green over yellow independent of material (cardboard or leaves of Nasturtium officinale R. Br., Brassicaceae). Preference behaviour tested in a dual‐choice contact assay coincides with visual preferences, where adults prefer young, more nutritious leaves for feeding and oviposition. Furthermore, females discriminate between visual cues of green leaves and green cardboard, whereas males do not, indicating that females are more sensitive in colour discrimination. Differences in colour wavelength influence the choice of beetle behaviour more strongly than differences in intensity. Both sexes of P. cochleariae prefer volatiles of the host plant N. officinale, whereas only females respond to the main volatile compound 2‐phenylethyl isothiocyanate. Given a choice between visual and olfactory cues, males orientate towards the colour cues, whereas females do not show any preferences. In males, visual cues may thus override olfactory cues, whereas, in females, both are equally important, which may reflect different ecological requirements and/or physiological abilities.